Manufacture of steel articles.



STATES PATENT OFFICE.

' HE 'nLYIr. nownor'isEDEo'BD s'rA'rIoN, NEW YORK, ASSIGNOR TOTAYLOR-WHARTON IRON & sTEEL'coMPANY, 01* HIGH BRIDGE, NEw JERSEY, ACORPORATION or NEW MANUFACTURE OF STEEL ARTICLES.

Specification of Letters Patent.

Patented Dec. 29, 1914.

g jn m' Application filed July 17, 1909, Serial No. 508,113. RenewedJuly 9, 1914. Serial No. 850,054.

To all whom it may concern:

Be it known that I, HENRY M. HOWE, a citizen of-the United States ofAmerica, residing at Bedford Station, in the county of WestchesterandState of New York, have invented certain new and useful Improvementsinthe Manufacture of Steel Articles, of which the following is a full,true, and concise specification.

The purpose of the present inventlon 1s the production of an integralsteel article havinga hardened exterior part-or surface especiallyadaptedto resistabrasion or wear, and a tough or ductile interiorespecially adapted to resist strain or shock, so that the article as awhole is adapted to resist simultaneously both wear'and shock and in asuperior degree.

The invention "is not concerned with the shape or nature of thesteelarticle and may be applied to any steel article wherein theseproperties are-of value; as, for example, to steel gear-wheels orpinions which are required to sustain strain and shock generally whiletheir teeth and bosses are specially required to resist Wear, or a ringor cylinder needing a hard inner surface. With such an article, or anyarticle, my invention contemplates the formation of the surface of thearticle or the part or parts which are to be subjected to the wearingaction, of steel a1- loy in the condition or'state known as martensite,and the remainder of the article, that is to say, its body or theinterior parts not intended to resist wear, of steel alloy in thecondition or state of austenite. By the term steel alloy I refer to allalloys of iron, other than the common white cast iron and graycast'iron. There is no general agreement as to the distinction betweencast iron and steel, and there may be some persons who would callcertain of the alloys to which I refer cast iron, while others wouldcall them steel. The essential thing in all of them is "that they arecapable of being made at will in part austenitic and in partmartensitic.

As is known to those skilled in this art,

there are three well marked states or conditions of steel alloys of thekind referred to; (*1) austenite, the normal non-magnetic conditionexisting spontaneously at and above a bright red heat; (2) pearlite, the

common magnetic state, in which all oui common slowly cooled iron andsteel objects exist; and (3) martensite, an intermediate state. Whensteel is heated to above a certam critical temperature called A03 andWlllCll varies from about 500 C. to about 900 C. with the composition ofthe steel, it passes spontaneouslyinto the austenite state.

'In cooling the austenite in general passes spontaneously either firstinto martensite and then into pearlite, which is the common constltuentof annealed carbon steel, or it may pass directly into the pearlitestate, skipplng over the martensite state. The temperature at which suchsteel becomes austenlte when the temperature is rising is called A03,and the temperature at which it passes out of the austenite state whenthe steel is cooling is called -Ar3. This Ar3 temperature is habituallysomewhat lower than Ac3, and, in case a very large percentage of nickelis present it may be very far below A03. When the steel alloy contains arelatively large percentage of the elements manganese and nickel which Iterm 01)- structive elements because they obstruct the escape from theaustenite and martensite conditions, these conditions have a relativelyfirm stability and remain austenite or martensite as the case may benotwithstanding that their cooling may occur very slowly and everyopportunity given for the change to take place, but where theproportions of these elements are less, the alloy tends to undergotransition through the successive stages above mentioned. By quicklycooling steel alloy of the kind just referred to while in the conditionof austenite, as by quenching it from far above A03 in cold water, theaustenitic formation or condition may be preserved in a state ofstability which, though not complete, is sufficient for many practicalpurposes. The rapidity with which the steel cools through the range oftemperature in which it is liable to shift from the austenite state intofirst that of martensite and from this into that of pearlite, (thetemperature below Ar3) increases with the temperature at which the steelis at the moment of quenching. The higher the quenching temperature thefaster does the steel cool through this range. Hence in order that thecooling through this range should be extremely rapid and that thequenching should have'the greatest effect in xing the austenite state,the steel when quenched. should be at a temperature far above A03. Forinstance, quenching small steel objects containing 2 per cent. of carbonand 2 per cent. of manganese in ice water from 1050 C. preserves them inthe austen ite state, whereas quenching from a temperature which thoughstill above Ac3 is yet much below 1050 C. would leave them in themartensite state. In the same way cooling them less rapidly, but stillrapidly, from 1050 0. would leavethem in the martensite state, andcooling them slowly would leave them in the pearlite state- Such lowertemperatures may be called martensitigenous and pearlitigenous resectively. The rate of cooling necessary to x these conditions is knownto the art, but quenching in a cold liquid is the most practical method.The presence of carbon adds to the obstructive effect of the elements,manganese and nickel.

In many cases the austenite thus produced and fixed is not pure but ismixed with martensite, and in other cases the martensite is diluted withaustenite. Therefore when I speak of steel in the austenitic state I donot refer solely to absolutely pure austenite, but I also include steelin which the proportion of austenite to martensite is such that theproperties of the steel as a whole are due in chief part to itsaustenite, pe'rhapsunavoidably or even in some cases advantageouslymodified by the accompanying martensite. So with my references to themartensitic state, mutatz's mutandz's. These conditions of steel alloysare readily distinguished andare well known to those skilled in thescience of metallurgy; generally they are regarded as different chemicalor mechanical combinations or solutions of the same elements of whichthe alloy has been prepared in the first instance.

Austenite is ductile or more accurately is shock-resisting. As-usuallyknown, in the steels very rich in manganese and nickel, it

is also very much harder than common steel in its annealed state, thoughless hard than hardened steel. But thishardness is prob "ably due to thepresence of the nickel and manganese respectively, because when steelpoor in manganese and mckel is brought to the austenitic state it isrelatively soft. The I hardness of such austenitic steel as determinedby the Shore scleroscope, is about that of annealed wrought iron. In themajority of cases included in this invention the'austenite is hard. Butits chief value lies in itspower of resisting shock abrasion. It resistsshock better than martensite. It resists abrasion better than pearlite,but not as well as martensite. Austenite is non-magnetic (in the senseof being very feebly magnetic), and appears under the microscope inordinary manganese steel of commerce containing about 12% maganese and14 carbon is an exampleof steel alloy consisting almost entirely ofaustenite, and another example is found in ordinary nickel steelcontaining about 25% nickel. 'Martensite on the other hand, is, muchharder than austenite, inore brittle, and appears under the microscopein the form of interlacing streaks or needles forming angular ortriirregular polygons. The

angular markings. Generally compared,

the difference between martensiteand austenite is of the same kind asthat between the case-hardened. and the non-case-hardened parts ofa soft"steel object, though the former difference is less marked" than 1 thelatter. A combination of "the austenitic and the martensitic states inone and the same object is more easily obtainable in steels containinglesser percentagesof manganese or of nickel than justabove stated.

In carrying out my invention I form the article in the first instance bycasting, forgin or otherwise, of steel or iron alloy of the kindreferred to; that is to say, having a composition which makes it capable.of existing in the states of austenite and martensite. to one ofseveralmethods so as to produce the martensitic condition in the part which Ithen treat the article accordlng' is to be made wear-resistive, and theaustenitic condition in the rest of the article. Themeans by which I' dothis are either I (1) to manipulate the temperature of the differentparts so as to produce austenite in the one part and martensite in theother; or (2) to shift the metal in part of the object into themartensite state by. mechanical deformation; or (3) to vary thecomposition relatively in the two .parts so as to make one part so richin the obstructive elements, manganese, nickel and carbon that it mayremain as austenite, and the wearresistive part less rich in theseobstructive elements so that it may slip into the martensite state underproper treatment; Or I may combine these different methods, using eachto reinforce the effect of the other.

The methods numbered (1'-) and (2) are evidently chiefly applicable tometal with a may be so unstable that it slips into themartensite state,while the rest is so stable that itcan be held in the austenite state.But I often reinforce the effects of local difl'erences iii com ositionby intentional differences in thermal treatment and in mechanicaldeformation;

In the case of the gear-wheel or pinion, the surface of the teeth isconverted into martensite and the remainder into austenite. The methodby which I prefer to produce the transformation in case of smallpinions, A and which I now proceed-to describe, is to quench the wholepinion from atemperature high enough to cause the whole of it to remaina-u'stenitic, and then to reheat the surface or wearing parts to atemperature at which they become martensitic, and then again to quenchthe whole, lest the change go too far and either too much of theaustenite changes into martensite, or too much of the martensite changesinto pearlite. In this way I fix the conditions of austeniteandmartensite in the respective parts in which they are severallyneeded; For example, the article made of say manganese steel containing2% manganese and 2% carbon, is first brought throughout its mass to atemperature well above the point A03 or say to 1050 (3., it beingunderstood 'that the actual temperature of A03 will vary somewhat withthe nature and ingredients of the steel alloy, and that the temperatureactually reached may vary in different parts of the piece, provided thatis well above A03. The point at which a particular steel becomesaustenite, however, is well known and easily determinable by thoseskilled in this art. The article is then plunged in ice water, in theway practiced in the treatment of the ordinary" manganese steel ofcommerce, except that for this specific composition the cooling shouldprogress the more rapidly, with the result that the entire articlebecomes austenite. I thereupon expose the article, or those portions ofit which are to be made of martensite, to a degree of heat and for ashort time, but suflicient to raise or bring the temperature of thesurface for a depth of about one-sixteenth of an inch more or less up toor above a temperature at which the particular steel alloy is known toshift over into the martensitic state. This temperature is always lowerfor a given alloy than that which produces austenite,

- and like that temperature it may be determined beforehand with asample of the alloy or after some experience may be gaged roughly withthe known alloy by the oxid color or the glow color as the case may be.An example of the time and temperature for a very small steel pinionhaving the above composition would be to heat its surface quickly to400, keeping the interior as nearly cool as practicable. By the glowcolor I refer to the colors such as dark blood red, cherry red, etc.,caused by the glowing of the object, as distinguished from the oxidcolers:

the surface thus transformed to the martensitic condition, the articleis again- I quickly cooled, as by plunging it into cold water, andtherebythe martensitic condition becomes fixed in the surface of thearticle or in such parts thereof as have been subjected to the surfaceheat and are desired to resist wear. The remainder is austenite,integrally joined to the martensite. While of itself a brittle andglassy-hard material, the martensite thus produced is disposed on thesurface of the article for a slight depth only, say one-sixteenth of aninch, and is so supported by the body of the austenite underneathit andinto which it merges, that its natural tendencies to crack or splinterunder shock or b'lows are quite avoided and the" article as a whole isexceedingly durable and ca able of long wear. A useful composition ortreatment in this manner may consist of manganese steel containing from6- per cent. of manganese and .85 per cent. car- 1 b'on to 9% manganeseand .75% carbon, intermediate percentages of manganese being used withproportional amounts of carbon.

Instead of first producing a uniform condition of austenite throughoutthe entire body of the article, it may be heated at one and the sametime up to an austenitigenous temperature and then the surface may beallowed to cool to a martensitigenous one, andthen by a single quenchingit may be preserved in these respective states. This I call adifferential quenching. If a certain part only of the article isrequired to be hard and wear-resistive, z. e. of martensite, all therest of it ma be heat-insulated so as to retard the coo ing except as tothat part which is left exposed and thus air cools more rapidly than therest of the article (but, of course, cooling at a rate incomparably lessthan that needed to retain austenite). When the faster cooling part hasreached the martensitigenous temperature, but while the slower coolingpart is still in the austenitigenous range of temperature, theseconditions are fixed in them by a single quenching.

Conversely, during the heating process the part or parts to be made ofmartensite may be heat-insulated or may be made thicker than the rest ofthe article exposed, whereby the two parts reach respectively themartensitigenous and austenitigenous temperatures at about the same timeor can be readily brought to such temperatures so that a single rapidcooling will fix these states and complete the process. If the heatingunder such conditions should produce in the more exposed part atemperature unduly above that of the rest, its exposed condition willpermit it to cool more rapidly than the insulated parts,- so that propertemperatures will be ultimately and simultaneously obtained in bothbefore quenching.

A further method of producing a similar shock and wear-resistive articleby a single sudden cooling and above referred to, consists in formingthe article uniformly of austenitic steel, and then, after it isestablished assuch, deforming the surface of the ficiently unstable toenable it to shift over cause the retention of the austenitic state intothe martensitic state simply by the mechanical deformation of rolling orotherwise working the suface of it, and without further heat treatment.

The effect of mechanical deformation is, as I believe, to relieve thepressure existing in the surface of the article. Pressure cooperateswith the obstructive elements, carbon, manganese, and nickel,'to retainthe metal in the austenite state; and tension or the release of pressureopposes them and favors the passage into the martensite state, for thereason that martensite is more bulky than austenite. The deformationwhich occurs for example in cold rolling produces local tensions attime, alternating'with local pressure. When the pressure is released orturned into tension the obstructive elements, no longer reinforced bythe pressure, may not suflice to hold a steel of moderate instability inthe austenite state, and it will in that case shift into the martensitestate. But the restoration of the pressure locally will not return themetal to the austenite state. Hence the alternations of pressure andtension which occur during cold deformation have theeflt'ect of changingaustenite into martensite.

A still further method consists of forming thearticle of a steel alloycapable of stable or fairly stable austenitic condition by reason of theproportions of its obstructive elements, and then by chemical actionlessening the proportion of these elements on the surface or on the,parts to be subjected to wear, so as to bring about conditions whichgive rise to martensite and thereafter quickly cooling the article by asingle quenching. For instance, a given percentage manganese steel witha moderate quantity of carbon shifts more readily from the austeniticinto the martensitic state than steel with more carbon. Hence, if asteel article containing enough carbon and mangenese jointly to during agiven treatment he superficially 'decarburized to a moderate extent byany usual method, for instance by heating it in contact with iron oxid,the outside of that object may be then shifted over into the martensiticstate while the inside remains in the austenitic state. When such anobject is cooled quickly from say..1100 (3., the outside will in coolingbecome martensitic, while the inside remains austenitic. If the coolingis so sudden as to retain even theoutside in the austenitic state, thenon slight reheating the outside will become martensite. An example ofthis method would be to heat manganese steel articles of 8.4% manganeseand 1.3% carbon, at say 950 C. for twelve hours in contact with ironoxid and sand and then raise it to 1100 C. and quench in cold water.

I claim the following:

1. An integral wear and shock resistive steel article having its wearsurface made of steel in the condition of martensite and the remainderor body portion of steel in the condition of austenite.

2. An integral wear and shock resistive article formed of an alloy ofmanganese, iron and carbon, and having its Wear sur- 9o face fixed inthe condition of such alloy known as martensite and the remainder in thecondition of austenite. I

3. A Wear and shock-resistive steel article having a portion of itswearing face for a depth of approximately inch made steel alloy in thecondition of martensite and the remainder of the article of steel in thecondition of austenite.

4. A method of making wear and shock resistive steel articles whichconsists in treating the surface portion of the article to producetherein the condition of martensite and the rest of the article toproduce therein the condition of austenite.

5. A method of manufacturing surfacehard steel articles whichconsists'in forming the article of asteel-alloy capable of theaustenitic condition and subsequently treating the article to producethe martensitic condition on its surface and the austenitic conditionthroughout its interior.

6. A method of manufacturing surface hard steel articles, which consistsin forming the article of a metallic alloy capable of existing in thestates of austenite and martensite and subjecting the surface andinterior of the said article to sudden cooling from temperaturesrespectively adapted to produce .the martensitic and austenitic statestherein.

7. A method ofmanufacturing wear and shock-resistive steel articleswhich consists in forming the article of manganese steel containingupward of five per cent. manganese, and subjecting the surface partsdesired to be wear resistive, and the remainder of the article,respectively, to sudden cooling from temperatures respectively adaptedto produce the martensitic and austenitic conditions of manganese steeltherein.

of moderate deptlrto shift over to the state of martensite and thenfixating such state by cooling the article. V

In testimony whereof, I have signed my 15 name to the specification inthe presence of two subscribing witnesses.

HENRY M. HOWE.

Witnesses:-

HELEN M. Eiownir, H. G. KIMBALL.

